Parmigiano Reggiano is made with milk, salt, and rennet only, so why can older pieces taste more savory or spicy without extra seasoning?

Answer: Aging breaks milk proteins into smaller pieces that taste savory.

Aging breaks milk proteins into smaller pieces that taste savory. ✓ — Right: the short ingredient list hides a long internal change. During aging, enzymes break milk proteins into peptides and free amino acids. Those smaller pieces taste savory and add depth, so older wheels can seem more savory and spicy even though nothing new is added.

Extra salt is rubbed into the rind while the wheel ages. — Extra salt would be an easy way to make an older wheel taste stronger, and saltiness does rise as the cheese ages. But Parmigiano Reggiano's ingredient list stays milk, salt, and rennet; no extra salt is rubbed in during aging. The rise comes from molecules already in the milk being changed, not from new seasoning.

Water leaves the wheel, concentrating its salt and flavor. — Water loss is real, and it does concentrate salt and flavor while making the texture drier. It cannot by itself explain why aged wheels turn savory, nutty, and spicy rather than just saltier. The missing step is protein breakdown, which creates new savory compounds from the milk proteins.